The invention relates to a process for the assembly of at least two parts made from a composite material incorporating a ceramic or vitroceramic matrix reinforced by ceramic fibers. Composite materials having ceramic or vitroceramic matrixes are being used with increasing frequency in the manufacture of parts simultaneously having to have a good resistance to high temperatures and a low weight. These materials are more particularly used in the manufacture of parts located in the hot areas of an aircraft turbo-jet engine. These parts are e.g. jet pipe flaps, reheat jet nozzle sleeves or arms, ferrules, collars, exhaust casing arms, blades or platforms for straighteners of a compressor or blades and mobile blade roots. These parts subject to stresses of a wide range of different types can break and it is then necessary to repair them.
Moreover, during the manufacture of large parts such as ferrules, it is frequently necessary to subdivide them into small individual components, bearing in mind the limits of installations used or the production processes and then assemble them (instead of carrying out an overall manufacture of the part).
The term "assembly process for two parts" therefore covers both cases referred to hereinbefore, i.e. not only the assembly, but also the repair of the parts.
The assembly of two or more parts made from the materials referred to hereinbefore causes problems if it is carried out by conventional mechanical means such as rivets, bolts or screws. Thus, mechanical assembly requires the drilling of the two parts to be assembled. However, it is difficult to machine ceramic composite materials as a result of their very great hardness and/or the presence of an anti-oxidation material layer on their surface or any other covering intended to protect the composite material. This covering tends to scale off or crack around the drill hole and therefore no longer fulfills its protective function against destructive external phenomena.
Moreover, when drilling takes place on a fiber-reinforced ceramic material, it has the effect of destroying a certain number of fiber strands, which reduces the mechanical strength of the part at said drill hole.
Finally, the presence of metal elements such as bolts or screws within the composite material part induces thermal expansion differences, which are prejudicial to the integrity of the assembly. It is therefore desirable to assemble the composite material parts with the aid of a material of the same type.
U.S. Pat. No. 4,353,966 describes a process for the joining of objects made from a composite material based on a glass matrix reinforced with carbon fibers. This process consists of applying to the surface of at least one of the two objects to be assembled, a glass mixture having a low softening point and a material with a high softening point and a low thermal expansion coefficient. The two objects are then assembled and hot compaction takes place.
U.S. Pat. No. 4,724,020 also discloses a process for the assembly of ceramic elements by heating and then applying a high voltage. More specifically, two torches are arranged on either side of the elements to be assembled and the contact line between the two elements is heated with the aid of these torches. A voltage between 1000 and 10,000 volts is then applied between these two torches. This process is applicable to ceramics conducting electricity at high temperature.
Finally, U.S. Pat. No. 4,156,051 discloses a process for the production of ceramic parts having complex shapes. These parts are e.g. the different elements of a turbine rotor. This process consists of producing a plurality of components of the final part by molding a ceramic material such as silicon nitride, aluminum nitride or silicon carbide, each component having a density above 98% of the theoretical value and a high bending strength. These components are then directly assembled with one another without intermediate foreign material by hot compaction. The bending strength of the joined parts is equal to that of the other parts of the component.
These processes are not suitable for the assembly of parts incorporating ceramic fiber reinforcements. Thus, during assembly, it is preferable to retain the continuity of the material at its junction for specific strength reasons.